12,241 research outputs found
Lessons Learned from the Pioneers 10/11 for a Mission to Test the Pioneer Anomaly
Analysis of the radio-metric tracking data from the Pioneer 10/11 spacecraft
at distances between 20--70 astronomical units (AU) from the Sun has
consistently indicated the presence of an anomalous, small, constant Doppler
frequency drift. The drift is a blue-shift, uniformly changing with rate a_t =
(2.92 +/- 0.44) x 10^(-18) s/s^2. It can also be interpreted as a constant
acceleration of a_P = (8.74 +/- 1.33) x 10^(-8) cm/s^2 directed towards the
Sun. Although it is suspected that there is a systematic origin to the effect,
none has been found. As a result, the nature of this anomaly has become of
growing interest. Here we discuss the details of our recent investigation
focusing on the effects both external to and internal to the spacecraft, as
well as those due to modeling and computational techniques. We review some of
the mechanisms proposed to explain the anomaly and show their inability to
account for the observed behavior of the anomaly. We also present lessons
learned from this investigation for a potential deep-space experiment that will
reveal the origin of the discovered anomaly and also will characterize its
properties with an accuracy of at least two orders of magnitude below the
anomaly's size. A number of critical requirements and design considerations for
such a mission are outlined and addressed.Comment: 11 pages, invited talk given at ``35th COSPAR Scientific Assebly,''
July 18-24, 2004, Paris, Franc
A Mission to Test the Pioneer Anomaly
Analysis of the radio tracking data from the Pioneer 10/11 spacecraft has
consistently indicated the presence of an anomalous small Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
The nature of this anomaly has become of growing interest in the fields of
relativistic cosmology, astro- and gravitational physics as well as in the
areas of spacecraft design and high-precision navigation. We present a concept
for a designated deep-space mission to test the discovered anomaly. A number of
critical requirements and design considerations for such a mission are outlined
and addressed.Comment: Final changes for publication. Honorable Mention, 2002 Gravity
Research Foundation Essay
Directly Measured Limit on the Interplanetary Matter Density from Pioneer 10 and 11
The Pioneer 10 and 11 spacecraft had exceptional deep-space navigational
capabilities. The accuracies of their orbit reconstruction were limited,
however, by a small, anomalous, Doppler frequency drift that can be interpreted
as an acceleration of (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed toward the Sun.
We investigate the possibility that this anomaly could be due to a drag on the
spacecraft from their passing through the interplanetary medium. Although this
mechanism is an appealing one, the existing Pioneer radiometric data would
require an unexpectedly high mass density of interplanetary dust for this
mechanism to work. Further, the magnitude of the density would have to be
nearly constant at distances ~ 20-70 AU. Therefore, it appears that such an
explanation is very unlikely, if not ruled out. Despite this, the measured
frequency drift by itself places a directly-measured, model-independent limit
of \lessim 3 x 10^{-19} g/cm^3 on the mass density of interplanetary dust in
the outer(~20-70 AU) solar system. Lower experimental limits can be placed if
one presumes a model that varies with distance. An example is the limit \lessim
6 x 10^{-20} g/cm^3 obtained for the model with an axially-symmetric density
distribution that falls off as the inverse of the distance. We emphasize that
the limits obtained are experimentally-measured, in situ limits. A mission to
investigate the anomaly would be able to place a better limit on the density,
or perhaps even to measure it.Comment: 16 pages, 2 figures, publication versio
The Pioneer Anomaly: The Data, its Meaning, and a Future Test
The radio-metric Doppler tracking data from the Pioneer 10/11 spacecraft,
from between 20-70 AU, yields an unambiguous and independently confirmed
anomalous blue shift drift of a_t = (2.92 \pm 0.44)\times 10^{-18} s/s^2. It
can be interpreted as being due to a constant acceleration of a_P = (8.74 \pm
1.33) \times 10^{-8} cm/s^2 directed towards the Sun. No systematic effect has
been able to explain the anomaly, even though such an origin is an obvious
candidate. We discuss what has been learned (and what might still be learned)
from the data about the anomaly, its origin, and the mission design
characteristics that would be needed to test it. Future mission options are
proposed.Comment: 16 pages, 7 figures, to be published in the AIP Conference
Proceedings of the 2nd Mexican Meeting on Mathematical and Experimental
Physic
The Pioneer Anomaly and Its Implications
The Pioneer 10/11 spacecraft yielded the most precise navigation in deep
space to date. However, their radio-metric tracking data has consistently
indicated the presence of a small, anomalous, Doppler frequency drift. The
drift is a blue-shift, uniformly changing with a rate of ~6 x 10^{-9} Hz/s and
can be interpreted as a constant sunward acceleration of each particular
spacecraft of a_P =(8.74 +/- 1.33) x 10^{-10} m/s^2. The nature of this anomaly
remains unexplained. Here we summarize our current knowledge of the discovered
effect and review some of the mechanisms proposed for its explanation.
Currently we are preparing for the analysis of the entire set of the available
Pioneer 10/11 Doppler data which may shed a new light on the origin of the
anomaly. We present a preliminary assessment of such an intriguing possibility.Comment: 7 pages, 2 figures. Invited talk given at the XXIst IAP Colloquium on
"Mass Profiles and Shapes of Cosmological Structures", Paris, France, July
4-9, 200
Gender Equity in Intercollegiate Athletics: Determinants of Title IX Compliance
Using new data on intercollegiate athletes, this article shows that recent improvement in Title IX compliance among NCAA Division I institutions was previously overestimated, and provides the first estimates of compliance in Divisions II and III. In addition, regression analyses investigate how institutional characteristics relate to the extent of non-compliance
Chameleon effect and the Pioneer anomaly
The possibility that the apparent anomalous acceleration of the Pioneer 10
and 11 spacecraft may be due, at least in part, to a chameleon field effect is
examined. A small spacecraft, with no thin shell, can have a more pronounced
anomalous acceleration than a large compact body, such as a planet, having a
thin shell. The chameleon effect seems to present a natural way to explain the
differences seen in deviations from pure Newtonian gravity for a spacecraft and
for a planet, and appears to be compatible with the basic features of the
Pioneer anomaly, including the appearance of a jerk term. However, estimates of
the size of the chameleon effect indicate that its contribution to the
anomalous acceleration is negligible. We conclude that any inverse-square
component in the anomalous acceleration is more likely caused by an unmodelled
reaction force from solar-radiation pressure, rather than a chameleon field
effect.Comment: 16 pages; to appear in Phys.Rev.
Synergistic efficacy of 405 nm light and chlorinated disinfectants for the enhanced decontamination of Clostridium difficile spores
The ability of Clostridium difficile to form highly resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is being developed for environmental decontamination within hospitals, however further information relating to its sporicidal efficacy is required. This study aims to establish the efficacy of 405 nm light for inactivation of C. difficile vegetative cells and spores, and to establish whether spore susceptibility can be enhanced by the combined use of 405 nm light with low concentration chlorinated disinfectants. Vegetative cells and spore suspensions were exposed to increasing doses of 405 nm light (at 70–225 mW/cm2) to establish sensitivity. A 99.9% reduction in vegetative cell population was demonstrated with a dose of 252 J/cm2, however spores demonstrated higher resilience, with a 10-fold increase in required dose. Exposures were repeated with spores suspended in the hospital disinfectants sodium hypochlorite, Actichlor and Tristel at non-lethal concentrations (0.1%, 0.001% and 0.0001%, respectively). Enhanced sporicidal activity was achieved when spores were exposed to 405 nm light in the presence of the disinfectants, with a 99.9% reduction achieved following exposure to 33% less light dose than required when exposed to 405 nm light alone. In conclusion, C. difficile vegetative cells and spores can be successfully inactivated using 405 nm light, the sporicidal efficacy can be significantly enhanced when exposed in the presence of low concentration chlorinated disinfectants. Further research may lead to the potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures
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